Purification of wet-process phosphoric acid
with methanol ahd ammohia

ABSTRACT

IMPROVED PROCESS FOR PARTIAL PURIFICATION OF MERCHANTGRADE WET-PROCESS PHOSPHORIC ACID WITH CO-PRODUCTION OF IMPURE PHOSPHORIC ACID OR SOLID FERTILIZER MATERIALS CONTAINING FORM 50 TO 95 PERCENT OF THE IMPURITIES ORGINALLY PRESENT IN THE CRUDE ACID. CRUDE ACID IS TREATED WITH FROM 2.5 TO 4.2 POUNDS OF METHANOL PER POUND OF P2O5 AND WITH FROM 0.26 TO 0.4 EQUIVALENTS OF A SOLUBLE AMMONIUM COMPOUND PER MOLE OF P2O5 TO PRECIPITATE MOST OF THE METALLIC AND FLUORINE IMPURITIES AND 7 TO 14 PERCENT OF THE P2O5 AS SOLID AMMONIUM METALIC PHOSPHATES AND FLOURIDE COMPOUNDS. THE REACTION MIXTURE IS MAINTAINED AT TEMPERATURES FORM 35*C. TO ITS BOILING POINT (ABOUT 70*C.) FOR 15 TO 90 MINUTES TO FORM SLURIES THAT FILTER AND SETTLE RAPIDLY. THE SOLIDS ARE SEPARATED FORM THE REACTION MIXTURE AND METHANOL IS DISTILLED FROM THE RESULTING CLARIFIED SOLUTION TO FORM CONCENTRATED PARTIALLY PURIFIED ACID. THE SOLID AMMONIUM METALLIC PHOSPHATES CONTAIN FROM 44 TO 54 PERCENT P2O5, ALL OF WHICH IS AVAILABLE,AND ABOUT 50 PERCENT IS WATER SOLUBLE BY AOAC PROCEDURES. ALTERNATELY, THE REACTION SLURRY IS SEPARATED INTO A CLARIFIED LIQUID FRACTION AND A SETTLED SLURRY FRACTION. METHANOL IS DISTILLED FROM THE SETTLED FRACTION, WHICH CAUSES MOST OF THE IMPURITIES TO REDISSOLVE, YIELDING IMPURE PHOSPHORIC ACID.



